1. Field
This disclosure relates generally to wireless communication systems and, more specifically, to techniques for reducing noise and interference in wireless communication systems.
2. Related Art
Today, many wireless communication systems are designed using a shared uplink (UL) channel. For example, in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 (commonly known as worldwide interoperability for microwave access (WiMAX)) and third-generation partnership project long-term evolution (3GPP-LTE) compliant architectures, a UL channel is shared and resources are periodically allocated to subscriber stations (SSs) by a serving base station (BS).
In a typical WiMAX compliant wireless communication system, when a user of an SS activates the SS, the SS searches for a downlink signal from a BS and attempts to coordinate with the BS when the downlink signal is found. If a recent downlink channel existed for the SS, the SS may attempt to reuse functional parameters associated with the recent downlink channel. When a recent downlink channel does not exist for an SS, the SS may examine various potential downlink channels in a downlink frequency band. When a downlink channel is selected, the SS attempts to synchronize with a transmission on the channel, e.g., by detecting cyclic frame preambles.
After time synchronization (between a BS and an SS) has been established at a physical (PHY) layer of the SS, the SS may continue to search for downlink channel descriptor (DCD) and uplink channel descriptor (UCD) messages that are periodically broadcast by the BS. The DCD and UCD messages include information about physical layer features of both the downlink and uplink channels. Among other information, the messages provide (to the SS) a modulation type and forward error correction (FEC) type employed by the BS. Depending on the physical specification selected for a given setting, the BS may periodically transmit uplink-map (UL-MAP) and downlink-map (DL-MAP) messages that describe burst start times for the channels. In a WiMAX compliant communication system, the BS also assigns SSs to the downlink and uplink channels through the DL-MAP and UL-MAP messages.
A WiMAX compliant SS transmits code division multiple access (CDMA) codes (to a BS) to achieve synchronization and receive an allocation from the BS. By the time an SS receives an assignment/allocation from a BS, it can be assumed that the SS has achieved synchronization (in both time and frequency) with the BS. After contention based ranging, an SS receives an uplink grant to send in a bandwidth request header to allow a BS to assign additional uplink grants to the SS. In the case of initial ranging, the BS provides an unsolicited allocation which the SS uses to send a WiMAX packet ranging request. The ranging process is part of framing and media access in IEEE 802.16 and includes initial ranging and periodic ranging. The early ranging contention slot is used for network entry (NE), In initial ranging, an SS sends a ranging request (RNG-REQ) message in a primary ranging contention slot. If the message is received correctly by the BS, the BS replies to the SS with a ranging response (RNG-RSP) message that provides timing and power correction information to the SS. The information in the ranging response message permits the SS to adjust timing and power of a signal that is to be transmitted (from the SS) to the BS.
In a typical implementation, the ranging response message also provides a connection ID (CID) assigned (by the BS) to the SS. In contrast to an initial ranging message, a periodic ranging message may be employed by an SS to send ranging-request messages to the BS in order to adjust power levels, time, and frequency offsets. After ranging is complete, the SS reports its physical layer capabilities (e.g. available modulation and coding schemes, whether frequency division duplexing (FDD) supports half-duplex or full-duplex, and/or whether time division duplexing (TDD) supports half-duplex or full-duplex) to the BS, which may accept or reject the reported capabilities. After reporting its capabilities, an SS may be authenticated and authorized by the BS. Typically, each SS is assigned a digital certificate, which is physically bound to hardware of the SS during manufacturing. Usually, a certificate of an SS includes a medium access control (MAC) address, e.g., a 48-bit MAC address, that a BS utilizes to authenticate the SS.
After authentication and authorization, the SS continues with the registration stage. In the registration stage, an SS sends a registration request message to the BS. The BS may respond with a registration response message that includes a secondary management CID for the SS and an Internet protocol (IP) version used for the secondary management CID. The receipt of the registration response message (from the BS) indicates to the SS that the SS has been registered in the network and is allowed to enter the network. Following registration, the SS can obtain an IP address through a dynamic host configuration protocol (DHCP), obtain current time information (e.g., through the Internet time protocol), as well as obtain other parameters from the BS.
A wireless communication system may implement an element management system (EMS) to manage elements and dynamically measure and optimize network performance. A typical EMS provides service and network management. For example, an EMS may be configured to provide a unified interface to manage and control elements (e.g., BSs, SSs, and gateways) of a radio access network (RAN) and quality-of-service (QoS) management for multi-application use. An EMS may also be configured to provide real-time performance monitoring (for radio network optimization) and configuration, alert, and alarm management. An SS may be configured to employ an over-the-air (OTA) option that facilitates channel power monitor measurement. In general, the OTA option allows power of a specific channel to be measured and analyzed by an SS. The OTA option may be utilized with a global positioning system (GPS) feature such that measurement data, which can include GPS location and time data for plotting on a map, may be reported for utilization in network management.